Apparatus for adjusting the thread feed rate of a circular knitting machine

ABSTRACT

An apparatus for adjusting the thread feed rate and hence the thread tension of a multiple-feed circular knitting machine includes transducer means in the form of a resiliently biased rocker mountable on the machine. The rocker can operate one of two microswitches whenever the tension of a thread engaging the transducer is greater than a predetermined value and can operate the other when it is less than the predetermined value. The microswitches control the energization of a servomotor operable to increase or decrease the speed of a rotary drive for driving the machine&#39;s thread feed device as necessary in order to bring the thread tension to the predetermined value.

The present invention relates to apparatus for adjusting the thread feed rate of a multiple-feed circular knitting machine, of the type including a first rotary drive, which in known machines comprises the principal motor, for driving the needle actuating mechanism, normally a needle cylinder of the machine, at a predetermined speed, and a second common rotary drive for driving the thread feeds of the machine at a speed which is variable with respect to that of the first rotary drive.

In knitting machines of the aforesaid type, the take-up of threads by the needles varies considerably according to the type of fabric being produced such that it is necessary to adjust the ratio between the thread-feed rate and the working speed of the machine for each type of fabric. In a known machine of the aforesaid type this adjustment is carried out by means of a change-speed gear or adjustable ratio transmission device, forming part of the second rotary drive, which drives the drive pulley of a belt transmission which includes as many driven pulleys as there are thread feeds. In another very widely used machine, the drive pulley of the belt transmission is of variable diameter and constitutes the adjustable ratio transmission device.

These known solutions all have the disadvantage, however, of being considerably difficult to adjust since the adjustment relies on the judgment of the operator. Moreover, the adjustment can only be effected when the machine is stopped and, since adjustment is effected by trial and error, the machine must be restarted after each adjustment attempt in order to check whether the thread tension is correct. In view of the slight probability of producing the correct thread tension at the first adjustment attempt, it is almost inevitable that when the machine is started up thread breakages occur due to excess tension.

An object of the present invention is, therefore, to provide apparatus for adjusting the thread feed rate of a circular knitting machine of the above-mentioned type which can be used to adjust the thread feed rate, and consequently the thread tension, to the correct value, automatically at the start of working, without it being necessary to undertake adjustment by trial and error.

According to one aspect of the present invention there is provided apparatus for adjusting the thread feed rate of a multiple feed circular knitting machine of the type including a first rotary drive for driving the needle actuating mechanism of the machine at a predetermined speed and a second common rotary drive for driving each of the thread feeds of the machine at a speed which is variable with respect to that of the first rotary drive, characterised in that the apparatus includes

a transducer mountable on the machine to be sensitive to the tension of one of the feed threads and responsive to variations therein to generate first or second electrical signals respectively whenever the tension of the thread is either greater than or less than a predetermined value;

control means connectable to the second rotary drive and to the transducer, and operable to increase or decrease the speed of the second rotary drive, and hence the thread feed rate, on receipt of a first or second signal respectively in order to bring the tension of the threads to the said predetermined value; and

means for selectively enabling or disabling the said control means whereby to bring the apparatus into operation when required.

When in use in a multiple-feed circular knitting machine, the apparatus according to the invention allows the thread-feed rate to be adjusted automatically during operation of the machine to give a predetermined thread tension, the predetermined tension preferably being adjustable according to the type of knitting it is desired to carry out. Once a desired predetermined tension has been attained, knitting machines of the aforementioned type operate to maintain the tension and further adjustment is unnecessary and, in fact, undesirable as the apparatus according to the invention would correct for any slight variation in the tension in the thread being sensed, due, for example, to knots or lumps; this would give rise to a temporary variation in the feed rate of all the threads and the resulting knitted fabric would not have the desired evenness. The machine operator would therefore preferably operate the said means for disabling the control means once the machine is operating with the desired thread tension.

In a preferred embodiment of the invention the transducer comprises a rocker element, for example, a pivoted lever, which carries a thread deflector member engagable with the said one thread to deflect it from its normal feed path, biasing means which urge the rocker element, in use, in the direction of greater deflection of the said one thread and two electrical switches located one on each side of the rocker element so that one is operated when the rocker element is displaced by a predetermined amount to one side of an intermediate position which it occupies when the thread deflected by the deflector member has the predetermined tension, and the other is operated when the rocker element is displaced by a predetermined amount to the other side of this intermediate position.

According to a further aspect of the invention there is provided a multiple-feed circular knitting machine, characterised in that it includes apparatus for adjusting the thread feed rate as described above.

One embodiment of the invention will now be more particularly described, by way of example, with reference to the accompanying purely diagrammatic drawings, in which:

FIG. 1 is a side elevational view of a circular knitting machine provided with apparatus according to the invention for adjusting the thread feed-rate;

FIG. 2 is a diagrammatic plan view from above of the machine of FIG. 1;

FIG. 3 is a diagrammatic perspective view, on a larger scale, of a transducer sensing forming part of the apparatus according to the invention shown in FIG. 1;

FIG. 4 is a hybrid diagram of the machine of FIG. 1; and

FIG. 5 is a hybrid diagram of a second circular knitting machine provided with the apparatus according to the invention shown in FIGS. 1, 3 and 4.

Referring to FIGS. 1 and 2 of the drawings, a multiple-feed circular knitting machine is shown, having a needle cylinder 22 and a thread feed device, generally indicated 10, including a plurality of spools 12 each of which forms part of an individual thread feed which also includes a pulley 14. All the pulleys 14 are engaged by a single drive belt 16 which, in use of the machine, is driven by means of a drive pulley 18, by a direct current electric motor 20, such that all the threads F are fed at the same rate from respective spools 12 via respective pulleys 14 to the needle cylinder 22.

Referring to FIG. 4 of the drawings, the machine of FIGS. 1 and 2 is shown diagrammatically and parts corresponding to those of FIGS. 1 and 2 are indicated with the same reference numerals, even though they may be shown differently for the sake of simplicity. The needle cylinder 22 of the machine is rotatable by means of a drive 48, shown in the conventional form of a rotatable shaft, which is connected to the principal motor 24 of the machine to be driven to rotate thereby. To the drive 48 there is connected a tachogenerator 50 which generates an electrical voltage of amplitude proportional to the speed of the principal motor 24, that is, to the speed of the machine. The tachogenerator 50 is connected, by means of a potentiometer 52, to one of the inputs of an electronic differential amplifier 54 having a power output.

Another tachogenerator 56 is associated with the drive which connects the direct current motor 20 to the thread feed device 10. This drive, which is also shown in the conventional form of a shaft, is indicated with the same reference number 16 as the belts of FIGS. 1 and 2. The tachogenerator 56, which generates an electrical voltage of amplitude proportional to the speed of the motor 20 and hence proportional to the speed of the threads F, is connected to the other input of the differential amplifier 54. The power output of the latter supplies, in its turn, the direct current motor 20. As will be understood, the circuit just described constitutes an electronic speed control circuit which renders the speed of rotation of the motor 20, and hence the feed rate of the threads F, dependent on the speed of the motor 24, that is, upon the speed of the machine. The transmission ratio of the control circuit can be adjusted by means of the potentiometer 52 which has adjustable threaded shaft or traverse screw 60 carrying a cursor 62, and is manually operable by means of a graduated knob 58, which can also be seen in FIG. 1, keyed on to the end of the shaft 60.

The machine of FIGS. 1, 3 and 4 is also provided with apparatus according to the invention for adjusting the feed rate of the threads F, comprising a transducer 26 and a reversible direct current servomotor 64 connected in a circuit with a switch 66. As shown in FIG. 1 of the drawings, one of the threads shown as F_(o), instead of passing directly from the feed device 10 to the cylinder 22, is deflected via the transducer 26 which is sensitive to the tension of the thread F_(o) and adapted to generate first or second electrical signals respectively whenever the tension of the thread F_(o) is either greater than or less than a predetermined value.

Referring to FIG. 3 of the drawings, a preferred embodiment of the transducer 26 is shown including a plate 28 fixed to the frame of the machine and a lever 32 pivotally mounted from the plate 28 for pivotal movement in a vertical plane about a pivot 30 intermediate its ends. The thread F_(o), which is fed in the direction of the arrows A, passes successively under a fixed thread deflector 34 mounted on the plate 28, over a movable thread deflector 36 carried at one end of the lever 32, and round a second fixed thread deflector 38 mounted on the plate 28. The thread F_(o) thus tends to pivot the lever 32 in a clockwise direction, as seen in FIG. 3. This pivoting is resisted by resilient biasing means comprising a torsion spring 40 connected between an arm of the lever 32 opposite the end carrying the deflector 36 and an anchorage 42 in the plate 28. The anchorage 42 is shown conventionally in the form of a screw inserted into a slot made in the plate 28.

The transducer 26 also includes two microswitches 44, 46, mounted on the plate 28, the switch 44 being above and switch 46 below the arm of the lever to which the spring 40 is attached. The switches 44, 46 are so located and the tension in the spring 40 is such that when the thread F_(o) has a predetermined value, the lever 32 will engage neither of the microswitches 44 and 46; when the tension of the thread F_(o) exceeds the predetermined value by a given amount, however, the lever 32 will engage and operate the microswitch 44 and when the tension of the thread F_(o) falls below the predetermined value by a given amount the lever 32 will engage and operate the other microswitch 46. The effect of operating one or the other microswitch 44 or 46 will be explained hereinafter.

For the purposes of calibration of the transducer 26 to vary the said predetermined value of the tension of the thread F_(o), the spacing of the microswitches 44, 46 from the lever 32 can be varied in a manner not illustrated and the tension of the spring 40 can also be varied by adjusting the position of the anchorage 42.

Referring to FIG. 4 of the drawings, the transducer 26 is shown in the conventional form of a deflector, the fixed contacts 44 and 46 of which, indicated by the same reference numerals as the respective microswitches 44, 46 of FIG. 3, are connected to supply the servomotor 64. The output shaft of the servomotor 64 is in turn connected to drive the shaft 60 of the potentiometer 52.

The connection of the contacts 44, 46 of the transducer 26 to the servomotor 64 is such that when the microswitch 44 is operated due to the tension of the thread F_(o) being greater than a predetermined value, the servomotor 64 is made to rotate in the direction of increase of the transmission ratio of the electronic speed control circuit, whereby the speed of the motor 20 and hence the thread feed rate are increased, the tension of the threads being decreased; the microswitch 44 continues to activate the servomotor until the tension of the thread F_(o), and hence all the threads F, has fallen to the predetermined value. When the microswitch 46 is activated due to the tension of the thread F_(o) being less than the predetermined value, the servomotor is made to rotate in the opposite direction, thus increasing the thread tension until the predetermined value is achieved.

In use of the machine and apparatus of FIGS. 1 to 4, the positions of the microswitches 44, 46 and/or the tension of the spring 40 are first adjusted so as to determine a desired value of the tension of the thread F_(o), and hence all the threads F, for a particular knitting operation and at which the switches will not be operated. The machine may then be started and, due to operation of the microswitch 44 or 46, the tension of the threads F is quickly brought to the desired value. Thus the adjustment to constant tension of the threads F takes place with the machine in operation and breakage of threads is avoided.

Once the tension of the threads F has reached the desired predetermined value, this tension will be maintained by normal operation of the machine and operation of the switches 44, 46 will occur only when, for example, a flaw in the thread F_(o) causes a momentary change in its tension. Since it is undesirable for the tension of all the threads F to be adjusted to account for such fluctuations in the tension of one thread F_(o), the switch 66 may be opened by means of the knob 66 shown in FIG. 1 to disable the servomotor.

If, for any reason it is necessary to correct the tension of the threads, that is their feed rate, during the operation of the machine, the operator can turn the knob 58 of the potentiometer 52 manually.

Referring to FIG. 5 of the drawings, a second multiple-feed circular knitting machine fitted with apparatus as described above is shown. In the machine of FIG. 5, the electronic speed control circuit of the above machine is replaced by a mechanical, hydraulic, or other adjustable ratio transmission device of any suitable type, indicated 68.

In FIG. 5, the parts identical with those of FIG. 4 or having the same function, are indicated by the same reference numerals. Thus, the principal motor 24 is connected, by means of the drive 48, both to the needle cylinder 22 and to the input of the device 68, whilst the output of the latter is connected to the thread feed device 10 by the drive 16. The device 68 is furnished with a manual adjustment member 58 and with a shaft 70 connected to the servomotor 64 for varying the transmission ratio.

The operation of the apparatus according to the invention on the device 68 is as described with reference to FIGS. 1 to 4 and will not be described further. 

What is claimed is:
 1. Apparatus for adjusting the rate of feed, and hence the tension of the threads of a multiple-feed circular knitting machine of the type including:a needle actuating mechanism, a first rotary drive for driving said needle actuating mechanism at a predetermined speed, a plurality of thread feeds, and a second common rotary drive for driving each of said thread feeds at a speed which is variable with respect to that of said first rotary drive, said apparatus including:transducer means mountable on the machine to be sensitive to the tension of one of said feed threads and responsive to variations therein to generate first and second electrical signals respectively whenever the tension of said one feed thread is one of greater than and less than a predetermined value; means controlling said second rotary drive; means interconnecting in use said transducer means and said control means operating to feed said first and second signals to said control means; means interconnecting in use said control means and said second rotary drive, whereby the speed of said second rotary drive is increased on receipt by said control means of said first electrical signal and decreased on receipt by said control means of said second electrical signal respectively in order to bring the tension of said threads to said predetermined value; selective enabling means operable selectively to enable said control means whereby to bring the apparatus into operation when required; and said second rotary drive further comprising an electric motor having an electronic speed control circuit which receives an electrical input signal dependent on the speed of said first rotary drive, means incorporated in said electronic speed control circuit for adjusting the ratio between the speeds of said first and second rotary drives and means connecting said adjusting means to said control means.
 2. The apparatus of claim 1, wherein said means for adjusting the speed ratio comprise a potentiometer having a wiper and means for effecting displacement of said wiper and wherein mechanical means connect said reversible servomotor to said displacement means.
 3. The apparatus of claim 2, wherein said means for effecting displacement of said wiper of said potentiometer include an additional manual control member by means of which the speed of said second rotary drive can be adjusted when said control means are disabled. 